Syntheses, crystal structures and Hirshfeld surface analyses of N-arylsulfonyl derivatives of cytisine

Arylsulfonation of cytisine with three types of substituted arylsulfonyl chlorides produced products (I)–(III), the molecular structures of which differ in the location of the benzene fragment relative to the cytisine core. Intermolecular C—H⋯O hydrogen bonds cross-link the molecules into infinite chains.


Structural commentary
The conformations of the cytisine cores in structures (I)-(III) are virtually identical and also do not differ from that of the cytisine molecule itself (Freer et al., 1987), or its various N-derivatives. The configurations of the chiral C atoms in cytisine are 7R, 9S, whereas in the case of (I)-(III) obtained by arylsulfonation of cytisine, the configurations are 7R, 9R in each case.

Figure 1
The asymmetric unit of (I) with atom labelling. Displacement ellipsoids represent 30% probability levels. Table 1 Selected torsion angles ( ) for (I).

Figure 4
Overlay plot of the molecules in the crystal structures of (I)-(III).

Figure 5
The observed C5-HÁ Á ÁO1 hydrogen bond in the crystal structure of (I). For clarity, the disordered methyl fragment is not shown.

General method
Arylsulfonyl chloride (0.01 mol) and 10 ml of acetone were placed in a two-necked flask with a volume of 50 ml. After cooling, a previously prepared solution (1.9 g (0.01 mol) of  The observed hydrogen bonds (C4 0 -HÁ Á ÁO1) in the crystal structure of (III).

Figure 8
Three-dimensional Hirshfeld surfaces of the compound (I) plotted over d norm in the range À0.2931 to 1.5624 a.u., and Hirshfeld fingerprint plots for all contacts and decomposed into HÁ Á ÁH, HÁ Á ÁO/OÁ Á ÁH and HÁ Á ÁC/ CÁ Á ÁH contacts. d i and d e denote the closest internal and external distances (in Å ) from a point on the surface. Three-dimensional Hirshfeld surfaces of the compound (II) plotted over d norm in the range À0.2332 to 1.6350 a.u., and Hirshfeld fingerprint plots for all contacts and decomposed into HÁ Á ÁH, HÁ Á ÁO/OÁ Á ÁH, HÁ Á ÁC/CÁ Á ÁH and HÁ Á ÁCl/ClÁ Á ÁH contacts. d i and d e denote the closest internal and external distances (in Å ) from a point on the surface.

Figure 10
Three-dimensional Hirshfeld surfaces of the compound (III) plotted over d norm in the range À0.1815 to 1.3331 a.u., and Hirshfeld fingerprint plots for all contacts and decomposed into HÁ Á ÁO/OÁ Á ÁH, HÁ Á ÁH and HÁ Á ÁC/ CÁ Á ÁH contacts. d i and d e denote the closest internal and external distances (in Å ) from a point on the surface. cytisine and 0.01 mol of triethylamine in 15 ml of acetone) was added under stirring through a separatory funnel. The reaction mixture was stirred at room temperature for 10 h. The reaction mixture was then left in the open air overnight to produce a dry mass. The mass was treated with 15 ml of distilled water and the remaining solid filtered off and dried in air. The reaction scheme is shown in Fig. 11.
Colourless crystals of (I)-(III) suitable for X-ray analysis were obtained by slow evaporation of an ethanol solution.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 7. In (I), the methyl C8 0 atom is disordered over two positions (C8 0 A, C8 0 B). The site occupancy factors of the disordered fragment were refined with a free variable to a ratio of 0.55 (2):0.45 (2). Hydrogen atoms bonded to C atoms were placed geometrically (with C-H distances of 0.98 Å for CH, 0.97 Å for CH 2 , 0.96 Å for CH 3 and 0.93 Å for C ar ) and included in the refinement in a riding motion approximation with U iso (H) = 1.2U eq (C) or U iso = 1.5U eq (C) for methyl H atoms.

Data collection
XtaLAB Synergy, Single source at home/near, HyPix3000 diffractometer Radiation source: micro-focus sealed X-ray tube, PhotonJet (Cu) X-ray Source Detector resolution: 10.0000 pixels mm -1 ω scans Absorption correction: multi-scan (SADABS; Krause et al., 2015) T min = 0.032, T max = 1.000 17786 measured reflections 3553 independent reflections 3348 reflections with I > 2σ(I)  (9) Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.